The present invention relates to coating apparatuses and methods of applying coatings.
Coatings are utilized in a variety of settings to provide a variety of benefits. For example, modern gas turbine engines can include thermal barrier coatings (TBCs), environmental coatings, etc. to help promote efficient and reliable operation. Application of coatings can involve a variety of different application methods, such as plasma-based physical vapor deposition (PVD). When TBCs are applied to gas turbine engine components, such as blades and vanes, using plasma-based-PVD, the components being coated are rotated within a process chamber while a plasma stream directs a vapor stream of the coating material at the components. Examples of such known coating processes are disclosed in U.S. Pat. No. 7,482,035 and in U.S. Pat. App. Pub. Nos. 2007/0259173A1 and 2008/0226837A1.
A significant problem with known plasma-based PVD processes is the loss of heat. Plasma-based PVD coating processes have substantial difficulty managing spontaneous nucleation of coating particles at the periphery of the coating material vapor stream. Such spontaneous nucleation occurs at the periphery of the vapor stream where temperatures become cool enough for the formation of liquid and/or solid ceramic particles. When liquid and/or solid ceramic particles impinge the work piece, those liquid and/or solid particles detrimentally interfere with the formation and growth of desirable TBC microstructure. Specifically, solid spherical particles become entrapped in the growing TBC and disrupt desired columnar growth of ceramic crystals. A similar problem occurs when liquid ceramic impinges against the work-piece during columnar crystal growth; the development of proper TBC microstructures is disrupted by the discontinuity that results from droplets of ceramic that adhere and freeze to the work piece.
One approach known in the art for providing temperature control involves passive thermal shielding. However, passive thermal shielding mitigates only off-axis heat loss to a relatively cold process chamber. Known passive thermal shielding may be insufficient to sufficiently maintain coating materials in a vapor state for deposition on work pieces.